Organometallics 2003, 22, 4999-5010
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Synthesis, Stereochemistry, and Reactivity of Group 4 Metal Complexes That Contain a Chiral Tetradentate Diamine-Diamide Ligand Jean-Franc¸ ois Carpentier,†,‡ Alfredo Martin,‡ Dale C. Swenson,‡ and Richard F. Jordan*,§ Department of Chemistry, The University of Chicago, 5735 S. Ellis Avenue, Chicago, Illinois 60637, and Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242 Received July 16, 2003
Ti and Zr complexes of the new chiral tetradentate diamine-diamide ligand (Me2PMEN)2are described (H2(Me2PMEN), 1 ) N,N′-dimethyl-N,N′-bis[(S)-2-methylpyrrolidine]ethylenediamine). The reaction of 1 with Zr(NMe2)4 affords (Me2PMEN)Zr(NMe2)2 (C2-2) which is shown by NMR to have effective C2-symmetry in solution. Addition of excess ClSiMe3 to C2-2 gives (Me2PMEN)ZrCl2 (3) as a mixture of two isomers, C2-3 (kinetic product) and C1-3 (thermodynamic product). An X-ray diffraction study of C1-3 revealed a distorted octahedral structure with a cis-amide/cis-chloride arrangement of ligands. Reaction of C1/C2-3 with MeLi yields (Me2PMEN)ZrMe2 (C2-4), which exists as a single C2-symmetric isomer in solution. The reaction of 1 and Zr(CH2Ph)4 affords (Me2PMEN)Zr(CH2Ph)2 (5), which can be isolated as a mixture of two isomers, C1-5 (kinetic product) and C2-5 (thermodynamic product). The Ti derivative (Me2PMEN)Ti(CH2Ph)2 (C2-6) was prepared similarly from 1 and Ti(CH2Ph)4. Compound 6 shows effective C2-symmetry in solution. An X-ray study of 6 revealed a C2symmetric distorted octahedral structure with a trans-amide/cis-benzyl arrangement of ligands. Iodinolysis of C2-6 followed by alkylation with MeMgCl leads to the unstable dimethyl derivative (Me2PMEN)TiMe2 (C2-7). Alkyl abstraction from C2-4, C1/C2-5, and C2-6 using [Ph3C][B(C6F5)4], [HNMe2Ph][B(C6F5)4], [HNMePh2][B(C6F5)4], or B(C6F5)3 affords cationic alkyl complexes, of which [(Me2PMEN)M(CH2Ph)][B(C6F5)4] (M ) Ti, 8; M ) Zr, 9) were isolated. In situ-generated 8 and 9 are moderately active ethylene polymerization catalysts.
Introduction Group 4 metal complexes that contain tetradentate nitrogen donor ligands, including porphyrins, tetraaza[14]-annulenes, and other tetradentate N-based macrocycles,1 have been studied extensively in the last decade.2 One driving force for this work is the interest in the design of nonmetallocene single-site catalysts for the polymerization of R-olefins.3 An attractive goal in this area is to develop chiral metal complexes that incorporate readily available chiral amide ligands for exploitation in stereoselective catalysis.4 Here we describe Zr and Ti complexes that incorporate the new tetradentate diamine-diamide ligand Me2PMEN2-, derived by double deprotonation of the parent tetraamine N,N′-dimethyl-N,N′-bis[(S)-2-methylpyrrolidine]ethylenediamine (H2(Me2PMEN), 1, Chart 1). The coordination of linear tetradentate N-based ligands to a hexacoordinate metal center can produce many geometrical and optical isomers.5 However, tetradentate ligands that incorporate defined chiral centers may * To whom correspondence should be addressed. Fax: (+1)773-7020805. E-mail:
[email protected]. † Present address: UMR 6509 CNRS-Universite ´ de Rennes 1, Institut de Chimie, 35042 Rennes Cedex, France. ‡ The University of Iowa. § The University of Chicago.
coordinate in a more selective manner. Several chiral tetraamines that contain two pyrrolidine groups, including H4(PMEN) and H4(PPM) (Chart 1), have been prepared previously, and Mn(III), Co(III), Rh(I), Ir(I), Ni(II), and Cu(II) complexes of these ligands have been characterized.6 (1) (a) Martin, A.; Uhrhammer, R.; Gardner, T. G.; Jordan, R. F.; Rogers, R. D. Organometallics 1998, 17, 382. (b) Black, D. G.; Swenson, D. C.; Jordan, R. F.; Rogers, R. D. Organometallics 1995, 14, 3539. (c) Uhrhammer, R.; Black, D. G.; Gardner, T. G.; Olsen, J. D.; Jordan, R. F. J. Am. Chem. Soc. 1993, 115, 8493. (d) Giannini, L.; Solari, E.; De Angelis, S.; Ward, T. R.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem. Soc. 1995, 117, 5801. (e) De Angelis, S.; Solari, E.; Gallo, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Inorg. Chem. 1992, 31, 2520. (f) Floriani, C.; Ciurli, S.; Chiesi-Villa, A.; Guastini, C. Angew. Chem., Int. Ed. Engl. 1987, 26, 70. (g) Cotton, F. A.; Czuchajowska, J. Polyhedron 1990, 9, 2553. (h) Oberthu¨r, M.; Arndt, P.; Kempe, R. Chem. Ber. 1996, 129, 1087. (i) Fuhrmann, H.; Brenner, S.; Arndt, P.; Kempe, R. Inorg. Chem. 1996, 35, 6742. (j) Housmekerides, C. E.; Ramage, D. L.; Kritz, C. M.; Shontz, J. T.; Pilato, R. S.; Geoffroy, G. L.; Rheingold, A. L.; Haggerty, B. S. Inorg. Chem. 1992, 3, 4453. (k) Hagadorn, J. R.; Arnold, J. Angew. Chem., Int. Ed. 1998, 37, 1729. (l) Scott, M. J.; Lippard, S. J. J. Am. Chem. Soc. 1997, 119, 3411. (m) Brand, H.; Arnold, J. Coord. Chem. Rev. 1995, 140, 137. (n) Brand, H.; Capriotti, J. A.; Arnold, J. Organometallics 1994, 13, 4469. (o) Morton, C.; Gillepsie, K. M.; Sanders, C. J.; Scott, P. J. Organomet. Chem. 2000, 606, 141. (p) O’Shaughnessy, P. N.; Gillepsie, K. M.; Morton, C.; Westmoreland, I.; Scott, P. Organometallics 2002, 21, 4496. (q) Westmoreland, I.; Munslow, I. J.; O’Shaughnessy, P. N.; Scott, P. Organometallics 2003, 22, 2972. (r) Male, N. A. H.; Skinner, M. E. G.; Bylikin, S. Y.; Wilson, P. J.; Mountford, P., Schro¨der, M. Inorg. Chem. 2000, 39, 5483. (s) Skinner, M. E. G.; Li, Y.; Mountford, P. Inorg. Chem. 2002, 41, 1110.
10.1021/om0340443 CCC: $25.00 © 2003 American Chemical Society Publication on Web 10/28/2003
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able (S)-(2-hydroxymethyl)pyrrolidine; (ii) the (Me2PMEN)2- ligand is flexible and therefore should be able to coordinate to a variety of metals; and (iii) H2(Me2PMEN) has C2-symmetry, which may lead to C2-symmetric structures for (Me2PMEN)MX2 complexes. Assuming an ideal octahedral arrangement, 12 (Me2PMEN)MX2 isomeric structures are possible (A-L, Chart 2), of which four have C2-symmetry. These structures differ in the arrangement (cis vs trans) of the pairs of amide and X ligands and in the configuration of the amine nitrogens. Results and Discussion
The new ligand (Me2PMEN)2- was designed by modification of H4(PMEN)7 considering the following features: (i) H2(Me2PMEN) is readily prepared in enantiomerically pure form starting from commercially avail(2) For related (R2N)2MX2 chemistry, see: (a) Andersen, R. A. Inorg. Chem. 1979, 18, 2928. (b) Andersen, R. A. J. Organomet. Chem. 1980, 192, 189. (c) Planalp, R. P.; Andersen, R. A.; Zalkin, A. Organometallics 1983, 2, 16. (d) Bu¨rger, V. H.; Wiegl, K. Z. Anorg. Allg. Chem. 1973, 398, 257. (e) Bu¨rger, V. H.; Neese, H. J. Z. Anorg. Allg. Chem. 1969, 370, 275. (f) Bu¨rger, V. H.; Kluess, C.; Neese, H. J. Z. Anorg. Allg. Chem. 1971, 381, 198. (g) Minhas, R. K.; Scoles, L.; Wong, S.; Gambarotta, S. Organometallics 1996, 15, 1113. (h) Herrmann, W. A.; Huber, N. W.; Behm, J. Chem. Ber. 1992, 125, 1405. (i) Horton, A. D.; de With, J. J. Chem. Soc., Chem. Commun. 1996, 1375. (j) Canich, J. M.; Turner, H.; W. World Patent 92/12162, 1992. (k) Bradley, D. C.; Chisholm, M. H. Acc. Chem. Res. 1976, 9, 273. (l) Shah, S. A. A.; Dorn, H.; Voigt, A.; Roesky, H. W.; Parisini, E.; Schmidt, H. G.; Noltemeyer, M. Organometallics 1996, 15, 3176. (3) For recent reviews on olefin polymerization catalyzed by group 4 nonmetallocene complexes, see: (a) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428. (b) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283. (c) Coates, G. W.; Hustad, P. D.; Reinartz, S. Angew. Chem., Int. Ed. 2002, 41, 2236. (4) For representative examples of group 4 metal complexes containing chiral bidentate diamido ligands, see: (a) Cloke, F. G. N.; Geldbach, T. J.; Hitchcock, P. B.; Love, J. B. J. Organomet. Chem. 1996, 506, 343. (b) Pritchett, S.; Gantzel, P.; Walsh, P. J. Organometallics 1997, 16, 5130. (c) Pritchett, S.; Woodmansee, D. H.; Gantzel, P.; Walsh, P. J. J. Am. Chem. Soc. 1998, 120, 6423. (d) Armistead, L. T.; White, P. S.; Gagne´, M. R. Organometallics 1998, 17, 216. (e) Tsuie, B.; Swenson, D. C.; Jordan, R. F.; Petersen, J. L. Organometallics 1997, 16, 1392. (f) Male, N. A. H.; Thornton-Pett, M.; Bochmann, M. J. Chem. Soc., Dalton Trans. 1997, 2487. (g) Flora, M. A.; Manzoni, M. R.; Baumann, R.; Davis, W. M.; Schrock, R. R. Organometallics 1998, 18, 3220. (5) For example, see the coordination chemistry of triethylenetetramine (triene): (a) Basolo, F. J. Am. Chem. Soc. 1948, 70, 2634. (b) Buckimgham, D. A.; Marzilli, P. A.; Sargeson, A. M. Inorg. Chem. 1967, 6, 1032. (c) Sargeson, A. M.; Searle, G. H. Inorg. Chem. 1967, 6, 787. (6) H4(PMEN), N,N′-bis[(S)-2-methylpyrrolidine]ethane-1,2-diamine; H4(PPM), N,N′-bis[(S)-2-methylpyrrolidine]propane-1,3-diamine. (a) Kitagawa, S.; Murakami, T.; Hatano, M. Inorg. Chem. 1975, 14, 2347. (b) Comba, P.; Hambley, T. W.; Lawrence, G. A.; Martin, L. L.; Renold, P.; Varnagy, K. J. Chem. Soc., Dalton Trans. 1991, 277. (c) Bernhardt, P. V.; Comba, P.; Hambley, T. W.; Martin, L. L.; Varnagy, K.; Zipper, L. Helv. Chim. Acta 1992, 75, 145. (d) Bernhardt, P. V.; Comba, P.; Gyr, T.; Varnagy, K. Inorg. Chem. 1992, 31, 1220. (e) Bernhardt, P. V.; Comba, P.; Hambley, T. W.; Sovago, I.; Varnagy, K. J. Chem. Soc., Dalton Trans. 1993, 2023. (f) Kim, D.-Y.; Lee, D.-J.; Heo, N. H.; Jung, M.-J.; Lee, B.-W.; Oh, C.-E.; Doh, M.-K. Inorg. Chim. Acta 1998, 267, 127. (g) Alcon, M. J.; Gutierrez-Puebla, E.; Iglesias, M.; Monge, M. A.; Sanchez, F. Inorg. Chim. Acta 2000, 306, 117. (h) Alcon, M. J.; Iglesias, M.; Sanchez, F.; Viani, I. J. Organomet. Chem. 2000, 601, 284. (i) Alcon, M. J.; Corma, A.; Iglesias, M.; Sanchez, F. J. Mol. Catal. A: Chem. 2002, 178, 253. (7) The nomenclature adopted for 1 follows that used for H4(PMEN)6a and accounts for the substitution of the two exocyclic NH residues by NMe groups.
Ligand Synthesis. The tetraamine (S,S)-H2(Me2PMEN) (1) was prepared from (S)-(2-hydroxymethyl)pyrrolidine as shown in Scheme 1. The reaction of 2 equiv of (S)-(2-iodomethyl)pyrrolidine with N,N′-dimethylethylenediamine affords the ditosyl derivative Ts2(Me2PMEN), contaminated by ca. 30% of the mono(pyrrolidinyl)ethylenediamine alkylation product.8 Reduction of this crude mixture by excess LiAlH4 affords 1 as a colorless oil in overall 32% yield after workup.8 Synthesis of (Me2PMEN)ZrX2 Complexes. The amine elimination reaction of 1 and Zr(NMe2)4 yields (Me2PMEN)Zr(NMe2)2 (C2-2) in 61% isolated yield as a white solid (Scheme 2).9 1H NMR data indicate that the yield of C2-2 is essentially quantitative, but the high solubility of C2-2 in hydrocarbons and chlorinated solvents reduces the isolated yield. 1H and 13C NMR data establish that 2 has C2-symmetry on the NMR time scale between -60 and 100 °C in toluene-d8 solution. The assignment of the 1H NMR spectrum of C2-2 (see Chart 1 for the Me2PMEN2- numbering scheme) was made on the basis of a COSY experiment. The H-5 resonances appear at δ 4.3 (ddd) and 3.3 (m), the latter overlapping with the H-2 resonance, the H-γ resonances appear as two doublets at δ 2.62 and 1.70, and the H-R resonances comprise two doublets of doublets at δ 2.25 and 2.20. A single Me2PMEN N-CH3 resonance is observed at δ 2.13 (6H). The 13C NMR spectrum contains seven resonances for the Me2PMEN2- ligand, consistent with C2-symmetry. Addition of excess ClSiMe3 to C2-2 gives (Me2PMEN)ZrCl2 (3), which was isolated in 61% yield as pale yellow crystals (Scheme 2). The yield of 3 is essentially quantitative according to NMR data,10 but again isolation is hampered by the high solubility of this complex. 1H NMR monitoring experiments show that the reaction proceeds via a monochloro intermediate, (Me2PMEN)ZrCl(NMe2), which is transformed to a C2-symmetric dichloride complex (C2-3). C2-3 is slowly transformed to a C1-symmetric isomer. The equilibrium ratio [C2-3]/ [C1-3] ) 13/87 is reached after 2 days in C6D6 at 23 °C.11 The two isomers of 3 are easily differentiated by 1H NMR spectroscopy. The pattern of H-5, H-2, H-γ, and (8) For a similar alkylation reaction and the subsequent reduction of the N-tosylamine see: Tuladhar, S. M., D’Silva, C. Tetrahedron Lett. 1992, 33, 2203. (9) (a) Bradley, D. C.; Thomas, I. M. Proc. Chem. Soc., London 1959, 225. (b) Bradley, D. C.; Thomas, I. M. J. Chem. Soc. 1960, 3857. (c) Chisholm, M. H.; Hammond, C. E.; Hoffman, J. C. Polyhedron 1988, 7, 2515. (d) Diamond, G. M.; Jordan, R. F.; Petersen, J. L. J. Am. Chem. Soc. 1996, 118, 8024. (10) The fact that 3 is formed quantitatively in the reaction of C2-2 and excess ClSiMe3 shows that the Me2PMEN amide groups are much less reactive than the NMe2 groups.
Chiral Tetradentate Diamine-Diamide Ligand
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Chart 2. Possible Isomers for Octahedral (Me2PMEN)MX2 Complexesa
a The four entries in the descriptor refer to the arrangement of amide ligands, the arrangement of X ligands, the configuration of Na, and the configuration of Nb, respectively. Note that the amine ligands must be cis.
Scheme 1
H-R resonances observed for C2-3 is very similar to that for C2-2. C2-3 exhibits one N-CH3 1H NMR resonance, while C1-3 exhibits two. The 13C NMR spectra of C2-3 and C1-3 exhibit seven and 14 Me2PMEN2- resonances, respectively. Molecular Structure of C1-(Me2PMEN)ZrCl2 (C1-3). The solid state structure of C1-3 was determined by X-ray crystallography and is shown in Figure 1. Selected bond distances and angles are given in Table 1. C1-3 has a highly distorted octahedral structure with a cis-amide/cis-chloride ligand arrangement (structure (11) Rate constants for the isomerization of C2-3 to C1-3 (k ) 0.087(2) h-1, k′ ) 0.013(2) h-1; r ) 0.99; determined in the presence of 2 equiv of Me2NSiMe3) and C1-5 to C2-5 (k ) 0.0261(3) h-1, k′ ) 0.0046(3) h-1; r ) 0.996) were determined from 1H NMR spectra assuming a reversible first-order reaction and using the relation ln(([A]0 - [A]∞)/ ([A]t - [A]∞)) ) (k + k′)(t), where [A]0, [A]t, and [A]∞ are respectively the concentration of the kinetic product (C2-3 or C1-5) at the beginning of the reaction, at time t, and at equilibrium, k and k′ are the forward and reverse rate constants, and r is the correlation coefficient. Emanuel, N. M.; Knorre, D. G. In Chemical Kinetics, Homogeneous Reactions; Wiley: New York, 1973; pp 165-168.
K, Chart 2). The N-Zr-N angles in the five-membered chelate rings (N(1)-Zr-N(7) 72.1(2)°, N(16)-Zr-N(10) 74.5(2)°, N(7)-Zr-N(10) 73.8(2)°) are much smaller than the ideal octahedral value due to the chelation, while the N(amide)-Zr-Cl angles are correspondingly larger (N(16)-Zr-Cl(1) 104.7(2)°, N(7)-Zr-Cl(2) 113.2(2)°, N(16)-Zr-Cl(2) 99.0(2)°, N(1)-Zr-Cl(2) 96.9(2)°). The Cl(1)-Zr-Cl(2) angle is 91.04(9)°. The geometry at the amide nitrogens is planar (∑(angles): N(1) 359.6°, N(16) 358.9°). The Zr-N(amide) distances (2.039(6) and 2.038(6) Å) are similar to those in other zirconium-amide complexes,4f,12 and the Zr-N(amine) distances are ca. 0.4 Å longer than those values. The Zr-Cl(2) bond (2.457(2) Å) is slightly shorter than the Zr-Cl(1) bond (2.510(2) Å), as expected from the difference in trans influence of the N(10) amino and N(1) amido groups. Synthesis of (Me2PMEN)ZrR2 Complexes. The addition of 2 equiv of MeLi to a benzene solution of C1-3 or a mixture of C1-3/C2-3 cleanly affords (Me2PMEN)ZrMe2 (C2-4), which can be isolated in moderate yield as colorless crystals (Scheme 2). The most convenient synthesis of C2-4 (overall yield 67%) is a one-pot synthesis directly from C2-2 without isolation of 3. Regardless of the isomer ratio of the starting material 3, only one C2-symmetric isomer of 4 is observed by NMR spectroscopy in benzene-d6 solution. The 1H NMR spectrum of C2-4 was assigned on the basis of COSY and NOESY experiments. The NOESY spectrum in(12) (a) Warren, T. H.; Schrock, R. R.; Davis, W, M. Organometallics 1998, 17, 308. (b) Gibson, V. C.; Kimberley, B. S.; White, A. J. P.; Williams, D. J.; Howard, P. J. Chem. Soc., Chem. Commun. 1998, 313. (c) Aoyagi, K.; Gantzel, P. K.; Kalai, K.; Tilley, T. D. Organometallics 1996, 15, 923. (d) Gue´rin, F.; McConville, D. H.; Vittal, J. J. Organometallics 1996, 15, 5586.
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Figure 1. Two views of the molecular structure of C1-(Me2PMEN)ZrCl2 (C1-3). The right view corresponds to structure K in Chart 2. Hydrogen atoms and disordered C(13′) and C(14′) are omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level. Scheme 2
Table 1. Selected Bond Lengths (Å) and Angles (deg) for C1-3 Zr(1)-N(1) Zr(1)-N(16) Zr(1)-N(7) N(16)-Zr(1)-N(1) N(16)-Zr(1)-N(10) N(1)-Zr(1)-N(10) N(16)-Zr(1)-Cl(2) N(1)-Zr(1)-Cl(2) N(10)-Zr(1)-Cl(2) N(16)-Zr(1)-N(7) N(7)-Zr(1)-Cl(1)
2.039(6) 2.038(6) 2.464(6) 97.7(2) 74.5(2) 87.5(2) 99.0(2) 96.9(2) 172.6(2) 147.0(2) 82.7(2)
Zr(1)-N(10) Zr(1)-Cl(1) Zr(1)-Cl(2) N(1)-Zr(1)-N(7) N(10)-Zr(1)-N(7) Cl(2)-Zr(1)-N(7) N(16)-Zr(1)-Cl(1) N(1)-Zr(1)-Cl(1) N(10)-Zr(1)-Cl(1) Cl(2)-Zr(1)-Cl(1)
2.415(6) 2.510(2) 2.457(2) 72.1(2) 73.8(2) 113.2(2) 104.7(2) 154.7(2) 87.3(2) 91.04(9)
cludes a correlation between the multiplet at δ 3.413.34 that corresponds to H-2 and one H-5, and one H-γ resonance (δ 2.78), which is consistent with either a type E structure (close H-2‚‚‚H-γ contact) or a type F structure (close H-5‚‚‚H-γ contact), but not with structure A or B (Chart 2). The 1H and 13C NMR Zr-CH3 resonances of C2-4 appear at δ 0.39 and 35.1, respectively. The reaction of 1 and Zr(CH2Ph)4 in toluene affords (Me2PMEN)Zr(CH2Ph)2 (5), which was isolated in 76% yield as a pale beige powder (Scheme 2).13 A 1H NMR monitoring experiment established that the reaction proceeds quantitatively within 15 min at room temperature in benzene-d6 with release of 2 equiv of toluene. (13) (a) Collier, M. R.; Lappert, M. F.; Pearce, R. J. Chem. Soc., Dalton Trans. 1973, 445. (b) Lubben, T. V.; Wolczanski, P. T.; Van Duyne, G. G. Organometallics 1984, 3, 977. (c) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell, I. P. Organometallics 1985, 4, 902. (d) Chestnut, R. W.; Durfee, L. D.; Fanwick, P. E.; Rothwell, I. P. Polyhedron 1987, 6, 2019. (e) Crowther, D. J.; Baezinger, N. C.; Jordan, R. F. J. Am. Chem. Soc. 1991, 113, 1455. (f) Tjaden, E. B.; Swenson, D. C.; Jordan, R. F.; Petersen, J. L. Organometallics 1995, 14, 371.
The kinetic product is a C1-symmetric complex, which is slowly and partially transformed to a C2-symmetric isomer. The equilibrium ratio [C1-5]/[C2-5] ) 15/85 is reached after 5 days in C6D6 at 23 °C.11 The Zr-CH2Ph 1H NMR resonances of C2-5 appear as two doublets at δ 2.45 and 2.11 (2JH-H ) 10.1 Hz), and the ortho-Ph resonance appears as a low-field doublet at δ 7.1. The Zr-CH2Ph 13C NMR resonance is observed at δ 67.1 with 1JC-H ) 117 Hz. These data are consistent with normal η1-bonding of the benzyl ligands.14 The 13C NMR spectrum of C1-5 displays two Zr-CH2Ph resonances each with 1JC-H ) 117 Hz, also consistent with η1-bonding of the benzyl groups. Synthesis of (Me2PMEN)TiX2 Complexes. Halide displacement and amine elimination routes did not prove useful for the synthesis of (Me2PMEN)TiX2 complexes. The amine elimination reaction of Ti(NMe2)4 and 1 in toluene at room temperature is complete within 3 h but gives a mixture of several products, of which the expected product (Me2PMEN)Ti(NMe2)2 accounts for only ca. 30% according to 1H NMR.15 As a result, this species could be isolated only in very low ( (Me2PMEN)Ti(CH2Ph)+ (8). None of these systems are active for 1-hexene polymerization under the conditions studied (0-23 °C, toluene or chlorobenzene solvent, or neat 1-hexene). Exposure of a toluene solution of C2-4 and [Ph3C][B(C6F5)4] (to generate (Me2PMEN)Zr(CH3)+) to 1.4 atm of ethylene at 23 °C (entry 1) results in an exothermic reaction, rapid (ca. 2 min) formation of solid polymer, and discoloration of the initially orange-yellow reaction mixture. These observations suggest that polymerization is rapid but that rapid catalyst deactivation also occurs; the average activity calculated over the whole experiment time is therefore a lower limit. The polymer produced under these conditions has a high molecular weight with a very broad multimodal molecular weight distribution, which may reflect the apparent complexity of the reaction of C2-4 and the activator (vide supra) and/or the changes in the reaction conditions during polymerization. Activation of 5 with [Ph3C][B(C6F5)4] or [HNMePh2][B(C6F5)4] in toluene produces catalysts that display similar ethylene polymerization activity and produce polyethylene with similar properties (entries 3 and 5). These results suggest that the same active species, i.e., 9, is generated in both cases. In contrast, the catalyst generated by the reaction of 5 with B(C6F5)3, presumed to be [(Me2PMEN)Zr(CH2Ph)][PhCH2B(C6F5)3], is less active than 9 (entries 3 and 5 vs 6). When the polymerization temperature is raised to 100 °C (entry 7), the activity of 9 increases and a polymer with a lower molecular weight and a narrower polydispersity (Mw/Mn ) 3.1, monomodal) is formed. When polymerizations are carried out in chlorobenzene in place of toluene, the activities of both 9 and “(Me2PMEN)Zr(CH3)+” decrease (entries 2 and 4). Visual observations (discoloration of reaction mixtures) suggest that catalyst deactivation is faster in chlorobenzene than toluene for zirconium species.
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Table 5. Ethylene Polymerization Dataa entry
catalyst precursor
activator
solvent
time (min)
yield (mg)
activityb
Mwf (103)
Mw/Mn f
Tm (°C)g
1 2c 3 4 5 6 7e 8 9
ZrMe2[Me2PMEN] (C2-4) ZrMe2[Me2PMEN] (C2-4) Zr(CH2Ph)2[Me2PMEN] (5)d Zr(CH2Ph)2[Me2PMEN] (5)d Zr(CH2Ph)2[Me2PMEN] (5)d Zr(CH2Ph)2[Me2PMEN] (5)d Zr(CH2Ph)2[Me2PMEN] (5)d Ti(CH2Ph)2[Me2PMEN] (C2-6) Ti(CH2Ph)2[Me2PMEN] (C2-6)
[Ph3C][B(C6F5)4] [Ph3C][B(C6F5)4] [Ph3C][B(C6F5)4] [Ph3C][B(C6F5)4] [HNMe2Ph][B(C6F5)4] B(C6F5)3 [HNMe2Ph][B(C6F5)4] [Ph3C][B(C6F5)4] [Ph3C][B(C6F5)4]
toluene C6H5Cl toluene C6H5Cl toluene toluene toluene toluene C6H5Cl
90 120 90 90 90 90 15 60 150
295 20 495 2σ(I))b wR2c max. resid density (e Å-3)
3870 2882 (0.0922)
C28H42N4Ti hexagonal P61 8.436(2) 8.436(2) 65.57(2) 4041(1) 6 1.190 0.339 0.13 × 0.13 × 0.09 red block 213 Enraf-Nonius CAD4 Mo KR, 0.710 73 1560 2.0-25.0 -1,10; -10,4; -77,53 7497 3089 (0.1158)
2021
1861
direct methodsa 1.032 0.0483 0.0834 0.42
direct methodsa 0.998 0.0535 0.0846 0.22
a SHELXTL-Plus Version 5, Siemens Industrial Automation, Inc., Madison, WI. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) [∑[w(Fo2 Fc2)2]/∑[w(Fo2)2]]1/2, where w ) [σ2(Fo2) + (aP)2 + bP]-1.
B(C6F5)4- (δ 149.1 (d, JC-F ) 226), 139.2 (d, JC-F ) 229), 137.1 (d, JC-F ) 243), 125.0 (m br)) were also observed. X-ray Structural Determinations. Data collection, solution, and refinement procedures and parameters are summarized in Table 6, and details are provided in the Supporting Information. The data processing, solution, and refinement were done using SHELXTL v5.0 programs. A pale yellow needle of C1-3 was selected, and a total of 3870 data were collected using θ/2θ scans. On the basis of preliminary examination of the crystal, the space group P212121 was assigned. Intensity standards were measured at 2 h intervals and showed no decay. Lorentz and polarization corrections, as well as a Gaussian absorption correction based on crystal dimensions, were applied. The C12-C13-C14-C15-N16 ring has two conformations; C12, C15, and N16 are common to both. Two positions of partial occupancy were included for C13 and C14 (C13′ and C14′ are the alternate sites; occupancy fraction ) 0.46(2) for C13 and C14, occupancy fraction ) 0.54(2) for C13′ and C14′). The C12-C13, C13-C14, and C14-C15 distances were restrained to be the same as the C12′-C13′, C13′-C14′, and C14′-C15′ distances, respectively. The rigid bond restraint was applied to the anisotropic thermal
parameters of the atoms of this ring. Additionally, because of near coincidence (C13-C13′ ) 0.270 Å), the thermal parameters for C13 and C13′ were constrained to be the same. The thermal parameters of C14 and C14′ were restrained to be similar due to their close proximity (C14-C14′ ) 0.681 Å). All non-hydrogen atoms were refined with anisotropic thermal parameters. All hydrogen atoms were included with the riding model using program default values. A red hexagonal plate of C2-6 was selected, and a total of 7497 data were collected using θ/2θ scans. Based on preliminary examination of the crystal, the space group P61 was assigned. Intensity standards were measured at 2 h intervals and showed no decay. Lorentz and polarization corrections and an empirical absorption correction based on three φ scans measured at 10° intervals were applied. The rigid bond restraint was imposed on the anisotropic thermal parameters of the ligand atoms. The crystal is merohedrally twinned (twin law ) 0 1 0, 1 0 0, 0 0 -1) and the fraction of twinning refined to 0.470(2). All non-hydrogen atoms were refined with anisotropic thermal parameters. All hydrogen atoms were included with the riding model using program default values. Ethylene Polymerization. Polymerization experiments were performed in a 250 mL Fischer-Porter bottle equipped with a magnetic stirring bar and externally heated with an oil bath as desired. In a typical experiment (Table 5, entry 3), the Fischer-Porter bottle was charged with the activator [Ph3C][B(C6F5)4] (40 mg, 43 µmol) and placed under 1 atm of ethylene (99.99%). A solution of 5 (25 mg, 48 µmol) in toluene (13 mL) was introduced via cannula. The ethylene pressure was increased to 1.4 atm (20 psi, maintained constant during the experiment), and the solution was stirred for 1.5 h. Ethylene was vented, the Fischer-Porter bottle was opened to air, and 5% solution of HCl in ethanol (60 mL) was added. The mixture was stirred for 30 min. The polymer was collected by filtration, washed with 5% aqueous HCl (60 mL) and acetone (2 × 10 mL), and dried under vacuum overnight (0.495 g; activity ) 5430 g PE/mol of activated Zr‚h‚atm). Gel permeation chromatography (GPC) analyses were performed on a Waters 150C chromatograph equipped with differential refractometer and viscometer detectors using a PL gel mixedbed column, and at 145 °C in 1,2,4-trichlorobenzene. DSC analyses were conducted on a Perkin-Elmer DSC-2 model calibrated using indium metal with a sweep rate of 10 °C/min from 25 to 200 °C.
Acknowledgment. This work was supported by the Department of Energy (DE-FG02-00ER15036) and Total Co. J.F.C. thanks the Centre National de la Recherche Scientifique for a sabbatical leave. Supporting Information Available: Tables of crystallographic data (positional and thermal parameters and bond distances and angles) for C1-3 and C2-6; data are also available for these compounds in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org. OM0340443
